Adaptation to Environment. 



313 



found in bloom where the surrounding soil had a tempera- 

 ture of 69° C. (156.2" F.). 



Regarding the adaptation of plants to various degrees of 

 heat, the general statement may be made that nowhere on 

 the earth is it too cold and nowhere too hot (except at the 

 mouths of volcanoes, etc.) for plants to live and grow, in 

 virtue of the adaptive capacity of their protoplasts. 



Fig. 163. 

 Alpine Soldanellas growing through the snow. After Kerner. 



197. The Atmosphere. — Variations in the pressure of 

 the atmosphere, so far as artificial experiments teach us, 

 bring about marked adaptive modifications. As the pres- 

 sure is diminished, the rate of growth increases, more 

 numerous branches are produced, and the leaves are larger. 

 These changes apparently bear a direct relation to the 

 diminished amount of oxygen ; for just as animals must 

 breathe faster at high elevations where the atmosphere is 



